The present invention concerns a lubricant composition for marine engines, in particular for four-stroke or two-stroke marine engines, whose use promotes fuel efficiency and which has good engine cleanliness properties, in particular crankcase cleanliness.
In the automotive field, on account of environmental concerns, it is increasingly sought to reduce polluting emission and to increase fuel efficiency. The type of engine lubricant for motor vehicles has an influence on these two phenomena, and so-called “fuel-eco” engine lubricants for motor vehicles have come onto the scene. It is chiefly the quality of the lubricant bases, either alone or in combination with polymers improving the viscosity index and/or friction-modifying additives, which imparts “fuel-eco” properties to a lubricant. The savings in fuel generated through the use of “fuel-eco” lubricants are essentially obtained on cold starts when the engine has not yet reached stable mode, and not at high temperature in stabilized mode. In general, fuel economy under the NEDC cycle (New European Driving Cycle) in accordance with European Directive 70/220/CEE is 5% for cold-starts (urban cycle), 1.5% for hot engine (extra-urban cycle) with an average economy of 2.5%.
Yet, in the field of marine lubricants, marine engines operate in stabilized mode and there are very few cold starts. The “fuel-eco” solutions adapted to motor vehicle engines are therefore not adapted for marine engines. In particular, the fuel efficiency obtained in the automotive sector cannot be obtained in the marine sector. In addition, the formulation of a “fuel-eco” lubricant must not be detrimental to the other performance levels of the lubricant. In particular, wear resistance, demulsibility, neutralizing capacity and engine cleanliness (piston and/or crankcase) must not be deteriorated. It would therefore be desirable to have available a lubricant for marine engine which allows reductions in fuel consumption, whilst maintaining intact the other performing aspects of the lubricant in particular engine cleanliness and more particularly crankcase cleanliness.